This section provides background information which is not necessarily prior art to the inventive concepts associated with the present disclosure.
Lift gates provide a convenient access to the cargo areas of hatchbacks, wagons, and other utility vehicles. Typically, the lift gate is hand operated, requiring manual effort to move the lift gate between open and closed positions. Depending on the size and weight of the lift gate, this effort can be difficult for some users. Additionally, manually opening or closing a lift gate can be inconvenient, particularly when the user's hands are full.
Attempts have been made to reduce the effort and inconvenience of opening or closing a lift gate. One solution is to pivotally mount gas struts to both the vehicle body and the lift gate and which are operable to reduce the force required to open the lift gate. However, gas struts also hinder efforts to subsequently close the lift gate, as the struts re-pressurize upon closing, increasing the effort required. Additionally, the efficacy of gas struts varies according to the ambient temperature. Furthermore, the use of gas struts still requires that the lift gate is manually opened and closed.
Automated power closure systems used to open and close vehicle lift gates are well known in the art and typically include a power actuator that is operable to apply a force directly to the lift gate to enable opening and closing thereof. For example, U.S. Pat. No. 6,516,567 discloses a power actuator that works in tandem with a gas strut. The power actuator comprises an electric motor mounted within the vehicle body that is coupled to a flexible rotary cable by a clutch. The flexible rotary cable drives an extensible strut that is pivotally mounted to both the vehicle body and the lift gate. Thus, the electric motor can be controlled to raise and lower the lift gate conveniently without manual effort. A controller unit is operable to control actuation of the electric motor and can be in communication with a remote key fob button or a button in the passenger compartment, providing additional convenience. However, this type of power actuator is not without its disadvantages. Specifically, the power actuator is comprised of multiple parts, each of which needs to be assembled and mounted to the vehicle separately, increasing costs. The vehicle body must be specifically designed to provide a space to house the electric motor. Due to the limited space available, the motor is small and requires the assistance of the gas strut. Additionally, because the power actuator is designed to work in tandem with a gas strut, the gas strut can still vary in efficacy due to temperature. Thus, the electric motor must be balanced to provide the correct amount of power with varying degrees of mechanical assistance from the gas strut.
U.S. Publication No. US2004/0084265 provides various examples of power actuators working in tandem with gas struts and several alternative examples of electromechanical power actuators. These electromechanical power actuators include an electric motor and reduction gearset coupled via a flexible rotary cable to a second gearset which, in turn, is coupled via a slip clutch to a rotatable piston rod. Rotation of the piston rod causes a spindle drive mechanism to translate an extensible strut that is adapted to be pivotally mounted to one of the vehicle body and the lift gate. The slip clutch functions to permit the piston rod to rotate relative to the gearset when a torque exceeding its preload is exerted on the lift gate so as to accommodate manual operation of the lift gate without damaging the electromechanical power actuator. More specifically, the slip clutch releasably couples the gearset to the piston rod whereby, during normal operation, powered opening and closing of the lift gate is provided. However, when a high level force is applied to the extensible strut which attempts to back drive the spindle drive mechanism in response to excessive or abusive manual operation of the lift gate, the slip clutch momentarily releases the drive connection between the piston rod and the gearset to avoid mechanical damage to the system. A helical compression spring is installed in the power actuator to provide a counter balancing force against the weight of the lift gate.
U.S. Publication No. US2012/0000304 discloses several embodiments of power drive mechanisms for moving trunk lids and lift gates between open and closed positions. The power drive mechanisms have an offset configuration employing an electric motor-driven worm gearset to rotate an externally-threaded jackscrew for translating an extensible strut. A slip clutch is shown to be disposed between an output gear of the worm gearset and the rotatable jackscrew. In addition, a coupler unit is provided between the motor output shaft and the worm of the worm gearset. The coupler unit includes a first coupler member fixed for rotation with the worm shaft, a second coupler member fixed for rotation with the motor output shaft, and a resilient spider interdigitated between fingers extending from the first and second coupler members. The resilient coupler provides axial and circumferential isolation between the first and second coupler members and functions to absorb transient or torsional shock loads between the motor shaft and the worm shaft.
In view of the above, it is evident that electromechanical drive mechanisms of the type used in trunk lid and lift gate powered closure systems are commonly equipped with a motor-driven gearbox. While such electromechanical drive mechanisms perform satisfactorily for their intended purpose, integration of these devices can increase the cost and complexity of powered actuators as well as impact the available vehicle packaging requirements.
It is therefore desired to provide an assembly for raising and lowering a vehicle trunk lid or lift gate that obviates or mitigates at least one of the above-identified disadvantages of the prior art.